BACKGROUND The aim of this study was to investigate the effects of red blood cell (RBC) storage duration on the outcomes of adult isolated traumatic brain injury (iTBI) patients after transfusion. MATERIAL AND METHODS A total of 1252 adult iTBI patients who received the fresh RBCs (stored for £14 days) or old RBCs (stored for >14 days) were finally enrolled in this study. The primary outcome was 90-day mortality. The secondary outcomes were in-hospital mortality, nosocomial infection, and complications. RESULTS By 90 days after RBC transfusion, 89 patients (17.0%) had died in the fresh RBC group, and 107 had died (14.7%) in the old RBC group, with no significant difference in 90-day mortality between the 2 groups (OR=1.192, 95% CI: 0.877-1.620, P=0.261). According to ISS score, no differences were discovered in mild injury (OR=1.079, 95% CI: 0.682-1.707, P=0.746), severe injury (OR=1.055, 95% CI: 0.634-1.755, P=0.838), and more severe injury (OR=1.940, 95% CI: 0.955-3.943, P=0.064). For GCS score, there were no differences in mild injury (OR=1.546, 95% CI: 0.893-2.676, P=0.118), moderate injury (OR=0.965, 95% CI: 0.616-1.513, P=0.877), and severe injury (OR=1.332, 95% CI: 0.677-2.620, P=0.406). We also observed no significant differences in secondary outcomes. CONCLUSIONS Use of old RBCs did not increase the 90-day mortality in adult iTBI patients.